Method of manufacturing seals for electric discharge tubes



Feb. 17, 1959 J. c. DURAN EIAL 2, 7

METHOD OF MANUFACTURING SEALS FOR ELECTRIC DISCHARGE TUBES Filed Sept. 6, 1955 Unite States METHOD OF MANUFACTURING SEALSFUR ELECTRIC DISCHARGE TUBES Application September 6, 1955, Serial No. 532,520

Claims priority, application Netherlands September 8, 1954 SJCEaEms. or. 29-15555 This invention relates to a method of manufacturing a seal for an electric discharge tube, and in particular to a seal comprising a contact member sealed in glass, with at least the surface of the contact member projecting from the tube consisting of gold or a gold alloy.

Although such gold-coated contact members can be sealed in glass satisfactorily if the coeficients of thermal expansion of the core material of the member and the glass correspond with one another, such contact members, particularly pinshaped members, suffer from the disadvantage that the glass is liable to crack when the member is subjected .to lateral forces. It was found that this was caused by insufficient adherence of the glass to the gold. It was known that the adherenceof the glass could be strongly improved if oxides are present on a metal surface. Hence, it has been proposed to coat the surface of copper-plated or silver-plated conductors with a thin layer of chromium, which during the scalingin process is entirely or partially converted into chromium oxide. Instead of chromium, onemay also use iron, aluminium, manganese or cobalt. However, in the present case, these metals have the disadvantage that they and their oxides can only be removed from the parts of the contact members projecting beyond the seal with difiiculty, particularly if they are coated over a layer of gold. In such contact members, the gold is employed to obtain a corrosion-resistant surface which makes a reliable contact with, for example, suitable contact springs. Consequently, this gold surface must be exposed and cleaned by removal of any oxides thereon. Further, it is also of importance that the oxide layer have a controlled thickness which is accurately determined, since an oxide layer which is too thick may give rise to leakage due to the fact that the oxide layer does not sufiiciently adhere to the base layer and is not entirely dissolved in the glass.

These requirements can be satisfied in a simple manner if, according to the invention, at the instant of scalingin of the contact member to the glass, thegold is provided with a layer of copper oxide, which, after the tube envelope has been sealed off, is preferably removed from the portion of the contact member which projects beyond the tube.

The copper oxide can be provided by coating the gold layer on the contact member with a copper layer, of, for example, from 5 to microns thick, which copper layer during the heating in the sealing-in process is en- I tirely oxidized to form copper oxide. This thin film of oxide also protects the base metal from attack by combustion gases and the like. The copper oxide film can subsequently be removed from the gold-plated parts of the contact member which project beyond the seal, together with any remaining copper, by pickling in a suit able bath of, for example, concentrated HCl, diluted with alcohol to about twice or three times its volume.

As an alternative, gold and copper may be coated att O 2,873,510 Patented Feb. 17, 1959 simultaneously on the core material of the contact member by electro-deposition. During heating in the scalingin process, a sufiicient amount of copper oxide is produced at the surface to ensure good adherence of the glass. The desired result is obtainable even if the layer contains only 1% of copper. In this event also, the oxides can subsequently be removed from the surface outside of the seal.

When not only a satisfactory contact but also a very high conductivity for high-frequency currents is required, the core material may be coated with a copper-gold compound, for example AuCu or AuCu The electric resistance of gold-copper compounds is a minimum at this molecular ratio. When such a compound is used, a surface copper oxide layer is produced during the sealing-in process, which subsequently can be readily removed from the surface projecting beyond the seal by pickling. Since such a layer of high electric conductivity contains a comparatively small amount of gold, it is cheap and consequently may be made comparatively thick without the tube becoming too expensive. This ensures better protection for the core metal. In addition, the wear resistance of such a layer is higher, not only because the layer is thicker but also because it is harder. On the other hand, in a known embodiment, care was taken to ensure that on no account was a copper oxide layer produced at the surface of a conductor adapted for carrying high frequency currents, since copper oxide is a semiconductor and the occurrence of largehigh-frequency losses was feared. To this end, the copper layer was coated with a layer of chromium, iron or aluminium, which layer was oxidized in order to improve the adherence of the glass, and which oxides ofier a very high resistance. As has been mentioned hereinbefore, the use of these metals involves the disadvantage that they and/or their oxides can only be removed from a gold surface with difiiculty.

One embodiment of the invention will now be described with reference to the accompanying drawing, of which the single figure shows an electric discharge tube manufactured by carrying out the process in accordance with the invention.

Reference numeral 1 designates the tube envelope, which is closed off by a base disc 2 made of glass, e. g. lead glass. In the disc 2 are sealed-in contact pins 3, which may, for example, consist of ferrochromium and are coated with a layer of gold 4. Between the gold layer 4 and the core 3, one or more inter-mediate layers, which preferably contain cobalt, may be interposed. At the seal, copper oxide 5 is dissolved in the glass so that satisfactory adherence of the glass to the gold layer 4 is obtained. The pins 3 are connected to an electrode system 6.

In the method of the invention, the pins 3, of chromeiron containing 25% chromium, are first coated with a gold layer of about 2 microns thick. Then, the pins are copper plated to a thickness of about 5 microns. The pins 3 are then mounted in apertures in the glass base 2, and the assembly heated at 800 C. for about 1 to, 2 minutes to cause thepins 3 to be fused vacuum-tight into the glass base 2. During this heating, sealing-in process, the copper layer is converted to copper oxide, which at the area of the seal dissolves partly in the glass to improve the adherence. Thereafter, the base 2 is sealed to the envelope 1 and the latter evacuated and sealed off. Then, the exposedends of the pins 3 are placed for a short time in a pickling bath, which readily removes the copper oxide layer on the pins 3, leaving a clean, gold surface on the portions of the pins projecting from the completed tube. This operation can be done as an alternative also to a ready performed tube.

While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art Without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of providing a metal contact member sealed in a glass wall ofa discharge tube, comprising the steps of coating said metal member with a layer consisting of AuCu; placing aportion of said coated metal member in contact with said glass wall; thereafter heating the member to. convert a portion of the copper in said AuCu into a thin external layer of copper oxide and simultaneously to fuse the member into the glass wall, and to dissolve in said glass substantially all of the copper oxide in the. seal region; and'thereafter removing the copper oxide from the portion of the member projecting from the Wall.

-2. A method of providing a metal contact member sealed in a glass wall of a discharge tube, comprising the steps of coating said metal member with a layer consisting of AuCu placing a portion of said coated metal member in contact with said glass wall; thereafter heating the member to convert at least a portion of the copper 'in said, AuCu into a thin'externa'l'layer of copper oxide and simultaneously to fuse the member into the glass wall, and to dissolve in said glass the copper oxide in the seal region; and thereafter removing the copper oxide from the portion of the member projecting from the wall.

3. A method of sealing a metal contact member con-- sisting essentially of an iron-nickel alloy in a glass wall of a discharge tube comprising the steps of coating said metal member with a layer of AuCu; placing a portion of said coated metal member in contact with the glass Wall; thereafter heating the coated metal member to convert a portion of the copper in said AuCu into a thin external layer of copper oxide and simultaneously to fuse the memher into the glass wall, and to dissolve in the glass substantially all of the copper oxide. in'the seal region; and thereafter'pickling the portionof the memberprojecting from, the glass Wall to remove the copper oxide therefrom.

4. A method of sealing a metal contact member consisting essentially of an iron-nickel alloy in a glass Wall of a discharge tube comprising the steps of coating said metal member with a layer :of a gold compound selected from the group consisting of AuCu and AuCu placing a portion of said coated metal member in contact with the glass; thereafter heating the coated metal member to convert a potrion of the copperin said gold-copper compound into a thin external layer of copper oxide and simultaneously to fuse the member into the glass wall, and

to dissolve in the glass substantially all of the copper oxide '7 in the seal region; and thereafter removing the copper oxide from the portion of the member projecting from the wall.

5. A method of sealing a metal contact member consisting'essentially of an iron-nickel alloy in a glass Wall of a discharge tube comprising the: steps of coating said metal member with a layer of AuCu yplacing a portion of said coated metal member in contact with the glass Wall; thereafter heating the coated metal member to convert a portion of the copper in said AuCu into a thin external layer of copper oxide and simultaneously to fuse the member into the glass wall, and todissolve in the glass substantially all of the copper oxide in the seal region; and thereafter pickling the portion-of the member projecting from theglass Wall to remove the copperoxide therefrom.

ReferencesCited in the'file of this patent UNITED STATES PATENTS 

1. A METHOD OF PROVIDING A METAL CONTACT MEMBER SEALED IN A GLASS WALL OF A DISCHARGE TUBE, COMPRISING THE STEPS OF COATING SAID METAL MEMBER WITH A LAYER CONSISTING OF AUCU; PLACING A PORTION OF SAID COATED METAL MEMBER IN CONTACT WITH SAID GLASS WALL; THEREAFTER HEATING THE MEMBER TO CONVERT A PORTION OF THE COPPER IN SAID AUCU INTO A THIN EXTERNAL LAYER OF COPPER OXIDE AND SIMULTA- 